Biology

Acipenser transmontanus, the scientific name for the white sturgeon, translates literally as sturgeon across the mountains. This tremendous fish is only found in two major rivers west of the Rocky Mountains in Canada. Both of these rivers flow in British Columbia – the Fraser (which includes the Nechako watershed) and the Columbia systems.

There had been speculation that the Nechako white sturgeon may have been part of the Fraser River population. But scientific studies in the late 1990’s have shown that Fraser and Nechako white sturgeon do not interbreed. Genetic samples (DNA) taken from sturgeon found in each waterway have shown that the Nechako white sturgeon is genetically unique, while tracking the giant fish through telemetry has shown that few Nechako sturgeon travel into the Fraser. Saving the Nechako white sturgeon is imperative in order to protect this irreplaceable population and maintain the whole species.

Its bizarre, pre-historic look and the rarity of encounters with this fish create much of the wonder surrounding the white sturgeon, which gets its name from the pale markings along its back and sides. In the lower Fraser River the white sturgeon can be massive, reaching 6 metres in length and weighing more than 800 kilograms. Individuals reaching this size may be more than 100 years old! In the Nechako system where growth is slower, a large sturgeon generally reaches about 3 meters in length. The long, streamlined body has no scales. Instead, it has bony plates, called scutes, arranged in five rows down its body. With a broad, flattened head, tiny eyes and shark-like tail, the sturgeon vaguely resembles a ferocious predator. Actually, the sturgeon is well adapted for bottom feeding. Its toothless mouth is on the underside of its head, and extends out of its body in order to suck up food. White sturgeon also have whiskers, or barbels, located between the snout and the mouth, which help it find edible objects.

Another factor that makes the white sturgeon so unusual is its reproductive habits. Sturgeon in the Nechako reach spawning age very late – around 20-25 years of age for males, and as late as 40 years for females. Once mature, females spawn more than once, but only every 3 to 10 years. This behaviour is one of the reasons why lack of juveniles in the Nechako River is so disturbing.

Sturgeon make up for their delayed and infrequent spawning by producing vast numbers of eggs, from about 700,000 in medium sized females to 3 or 4 million in the largest! It appears that preferred spawning sites have faster currents and rockier bottoms than feeding areas. Females and males migrate in loose groups and tend to spawn together in pairs where they release eggs and sperm into the swift water near the river bottom. The small, brown/black eggs quickly sink and filter into a porous riverbed where they stick to the rocks and are relatively safe from predators. Depending on water temperature, the eggs will hatch in 5 to 25 days, releasing larvae with yolk sacs attached, that are vaguely tadpole like in appearance. In about two weeks, the larvae become fry – miniature sturgeon complete with long snout and scutes. In the lower Fraser River, juveniles reach about 50 cm by age 5, and then grow about 5 cm per year until the age of 25. Nechako white sturgeon are believed to have a slower growth rate, due to the cooler temperatures, shorter northern summers and differences in the types of foods available.

Adult white sturgeon live entirely on animal matter. They primarily use touch and taste, rather than eyesight, to find food. They do this by following an odour, or simply by drifting in a prime location and waiting for the food to come by. Young sturgeon may snack on larval insects, freshwater clams and snails, while older sturgeon feed primarily on fish, including live adult salmon and even smaller sturgeon.

Adult sturgeon spend most of their time in large pools in the main channels of their home river and its tributaries, while young fish frequently move between main channels and nearby sloughs, especially during the summer months. Nechako white sturgeon have also been sighted in larger lakes such as Fraser, Takla, Trembleur and Stuart.